1. Field of the Invention
Embodiments of the present invention relate to a method for forming a metal pattern with a low resistivity. More particularly, embodiments of the present invention relate to a method for forming a metal pattern by sequentially forming a photocatalytic film layer composed of a photocatalytic compound (i.e., a compound whose reactivity is changed by light) and a water soluble polymer layer on a substrate, selectively exposing the two layers to light to form latent image centers for crystal growth by photoreaction, and plating the latent pattern with a desired metal to grow metal crystals on the latent pattern.
2. Description of the Related Art
With increasing demand for large display areas and flat panel displays with high resolution (e.g., liquid crystal displays (LCDs), plasma display panels (PDPs), and inorganic and organic luminescent displays (ELDs)), metal wirings are considerably extended in length. Furthermore, the design rule for increased aperture ratio is decreased. This creates several problems, such as a drastic increase in wiring resistance and capacitance as well as signal delay and distortion. Under these circumstances, the development of a process for forming metal wiring with a low resistivity is essential to developing high resolution and large area flat panel display devices.
The use of low resistivity aluminum (Al) as a wiring material has been actively discussed in large-sized LCDs. In this case, AlNd, an aluminum alloy, is used to prevent the problem of wiring non-uniformity (e.g., hillock, due to substance migration exhibited when pure Al is used). Because of an increase in resistivity caused by the addition of an alloy, however, and an increase in contact resistance by high reactivity with α-Si or ITO, a multilayer structure (e.g., Cr/AlNd/Cr) is required when an aluminum alloy is used as source/drain electrode material. However, complicated processes are required to form a multilayer metal pattern, which results in a productivity limitation.
Metals usable to form metal wirings of flat panel display devices are presented in the Periodic Table shown in Table 1 below:
TABLE 1
Aluminum alloys are currently used, but copper (Cu) and silver (Ag) have been the focus of intense interest. This is due to their low resistivity and good contact properties on an amorphous silicon layer. However, when copper or silver is used as a gate electrode, it exhibits poor adhesion to a lower substrate and thus the metal wiring tends to strip off during subsequent processes. Further, when copper or silver is used as a source or drain electrode, the atoms diffuse into an amorphous silicon layer at 200° C. or electromigration takes place due to electric drive. This causes deterioration in wiring and device properties. Accordingly, in order to use copper or silver as a wiring material having a low resistivity, there is a need to form an additional metal layer. The layer needs to have good adhesion to a substrate and a low contact resistance in the lower portion and/or the upper portion of the wiring material. This leads to a multilayer metal pattern.
In order to satisfy the need to form a large display area at a relatively low cost, it is therefore necessary to develop techniques capable of replacing conventional wiring materials with new materials such that multilayer metal wiring can be formed in a relatively simple manner.
Currently, metal patterns are formed using a photoresist. This method, however, involves complex processes, including metal sputtering, photoresist patterning and developing, and etching. It is accordingly not suitable for forming a multilayer metal pattern. In addition, there are substantial technical difficulties and increased manufacturing costs associated with the development of vacuum thin film deposition equipment for forming large area patterns on glass substrates of increased size.
U.S. Pat. No. 5,534,312 reports a method for forming a metal pattern without the necessity of an etching process. The method involves the following steps: coordinately binding an organic compound, which is susceptible to light, to a metal thereby producing an organometallic compound; coating the organometallic compound onto a substrate; and, irradiating the organometallic compound with light without application of a photosensitive resin. In this method, when the coated substrate is exposed to light through a patterned mask, the light directly reacts with the organometallic compound resulting in the decomposition of organic ligands coordinately bonded to the metal. The decomposition separates the ligands from the metal. The metal atoms react with adjacent metal atoms or ambient oxygen, and eventually a pattern of a metal oxide film is formed. The method is problematic, however, due to ligand contamination. Most of the ligands are separated by photoreaction in order to form the metal or metal oxide film. Furthermore, in connection with improving the electrical conductivity of the oxide film, the method disadvantageously involves reduction and surface annealing at 200° C. or higher for 30 minutes to several hours with a flow of a mixed gas of hydrogen and nitrogen.
Another method for forming a metal wiring by an ink-jet process is described in Japanese Patent Laid-open No. Hei 2002-169486. But, this method has problems of low resolution and difficult formation of highly electrically conductive wiring. Furthermore, U.S. Pat. No. 6,521,285 discusses the formation of metal wiring by micro-contact printing and electroless plating. This approach, however, has a disadvantage in that uniform metal wiring usable in a large area flat panel display device is seldom formed.
There is therefore a need in the art for a simple method that enables the formation of a multilayer metal pattern including a highly electrically conductive metal.